In recent years, the area of biomass-derived diesel fuels has drawn a great deal of attention. These fuels are plant and animal based and are produced from such sources as canola, corn, soybean etc. Biomass-derived fuels are generally environmentally less damaging to use than traditional fossil fuels.
Another potential source for biomass-derived diesel fuels is from the waste greases of animal rendering facilities and waste cooking oils, such as those found as restaurant trap greases. However these waste greases and oils tend to contain contaminants that must effectively be removed before processing.
In the past, catalytic hydrotreating has been performed on triglyceride feedstocks in an attempt to produce high-cetane diesel fuels. Examples of such processes can be seen in U.S. Pat. Nos. 5,705,722 and 4,992,605, herein incorporated by reference. The cetane value of a diesel fuel is a measure of how easily the fuel will auto-ignite at predetermined pressure and temperature and is often used to determine fuel quality. However, large quantities of hydrogen are required for this process, which is a major operating cost in the production of biomass-derived diesel fuel by catalytic hydrotreating. Reducing the volume of hydrogen consumed in the process would make the process economics more favourable. As well, hydrotreating was found to work best for very high quality feedstocks, such as tallow, vegetable oils (canola oil, soya oil, etc.) and yellow grease. Lower quality feedstocks, such as restaurant trap grease were found to be difficult to convert by catalytic hydrotreating, due to their heterogeneous nature and the presence of contaminants. These contaminants were found to rapidly deactivate the catalyst, thereby reducing hydrotreating reactor time on stream, requiring large quantities of catalyst to be used, and increasing operating costs. There is therefore a great need to find efficient methods of producing a high cetane value product from low quality waste triglyceride feedstocks, such as restaurant trap greases and other waste greases, which can be used as a diesel fuel or as diesel fuel blending stock. There is also a need to find efficient methods to reduce hydrogen consumption in the catalytic hydrotreating stage.